Friction brake



' April 7, 1942. P. A. ScoTT-NESEN 2,279,251

FRICTION BRAKE FiledAng. 22, 194C 2 Sheets-Sheet 2 atented Apr. 1942Pon! srs'rss ra'rsm'r ortica amarsi signor. to The Rover Campani',Limited, @o

entry, Engiand ppication .Mignot 22, ii, Sc'n Ho. 353,753

En Gren-t Britain r @mt Pr, 1939 is einen (er. rssresi or stops adaptedto hold the shoe or shoes inA4 constant contact with a complementarybrake member.

In the accompanying drawings- Figure 1 is a diagrammatic view of avehicle brake to which the invention is applicable.

sheets of explanatory Figures 2 to 6 illustrate respectively n ve o.lter-I native forms of the invention.

Figures "I and 8 are fragmentary views illusv trating respectivelymodications of the examples shown in Figures 4 and 5.

In Figure 1 a indicates a rotary drumwhich is provided around its innerperiphery with a .friction surface, and which is adapted to be mountedin the usual manner on a vehicle road wheel.

Within the drum a are pivotally mounted a pair of brake shoes b havingfriction surfaces adapted f to co-operate with the friction surface ofthe on the inner peripheral surface of the cylinder c. The ring m isarranged to fit the groove c closely so that little or no axial freedomexists tween the ring and piston. The frictional grip exerted by thering m on the cylinder c is made sufficient to prevent the shoe b frommoving out of contact with the drum a when the brake-applying force.hasbeen removed, but it is not sumcient materially toresist the.brake-applying force. The fre'e end of theshoeb is held in contact withthepston d either by gravity or by a spring (not shown) which acts inthe opposite direction to the brake applying force but is notsuiliciently strong to overcome the frictional grip of the ring m on thecylinder c when the brake-applying force is removed. In either case thebrake'is such that in the absence of the friction stops formed by therings as m the shoes b would tend to move away from the drum a when thebrake-applying force -is removed.

When' the brake is applied the shoes b areY pressed against the drum:Lin the usual manner for producing the requiredbraking eilect. OnAreleasing the brake, the shoes b do not, however, become separated fromthe drum a; but remain lightly in'contact with it, thel resistanceoffered by 'the shoes in this condition being insuillcient to cause anyinconvenience. Y

drum. Between the free ends of the shoes b there is mounted a ilxedhydraulic cylinderc containing a pair of oppositely movable pistons dadapted to exert pressure on the adiacent free ends of the shoes. At aposition between the pistons d the cylinder c is connected by a pipe eto `a cylinder f containing a piston g, the latter being operable by apedal h or other lever for exerting a brake-applying force on thepistons d through the medium of liquid contained in the cylinder f, pipee and cylinder c. When the piston y' is in its initial or idle positionas shown the interior of the cylinder l communicates through a pipe iwith a replenishing chamber j containing brake actuating'liquid, thiscommunication being interrupted by the piston gV when. the latter isactuated for applying the brake.

In applying the invention to the brake shown in Figure 1, Imay combinewith eachp ton d any convenient `friction device whereby t e piston canserve also as a stop for preventing retraction oi the corresponding shoeb from the drum a. Thus, as shown in Figure 2, I mount in acircumferential groove Ic in the piston d, a

It will be apparent that wear of the shoes b or drum a has no eiiect onthe movement required in the operating mechanism to bring the brake intoaction as the shoes are in constant contact with the drum. Moreover,contraction of the drum a on the shoes b due to a fall of temperaturehas no binding eil'ect .as the friction stops forrnedY by the rings as mallow the shoes to yield. Separation of the interacting surfaces of thedrum i a and shoes b due to expansion of the drum with a rise oftemperature is eliminated with'the next Ywall of the cylinder.

application of the brake-applying force.

ToY prevent leakage of uid between the cylinder c and pistons d, each ofthese pistons is embraced by a leather or other flexible packing 'ring oof channel section arranged in a. circumferential recess formed in theinner peripheral If desired the groove k formed in each pistond foraccommodating the corresponding spring ring m. may be o greater widththanthe ring, and a helical compression spring p may be arranged in thatpart of the groove not occupied by the ring as shown in Figure 3. thering being heid by' the spring in contact with the side of the v grooveremote from the corresponding shoe E: so

-- Spring ring m adapted to exert a frlctional grip ca that the actionof the' brakeapplyingforce has Y v no effect on the spring. the latterserving merely as a medium through which the ring serves to preventretraction of the shoe from the drum a. In this example leakage of fluidbetween the cylinder c and piston d is prevented by a leather or otherflexible packing disc q secured to the inner end of the piston andhaving a flanged peripheral portion in contact with the inner peripheralwall of the cylinder.

Instead of being mounted as above described in grooves in the pistons d,the spring rings as m may be mounted in circumferential grooves as lcformed around these pistons in the inner peripheral wall of the cylindercas illustrated in Figure 4, in which case each ring is adapted to exerta sufficient frictional grip on the corresponding piston to preventretraction of the adjacent shoe b without offering material resistanceto the brake-applying force. In other respects the exampleshown inFigure 4 is similar to that shown in Figure 2. But if desired the springring m shown in Figure 4 may be loaded by a helical compression springpV (similar to that Y.employed in Figure 3) arranged inthe groove kcontaining the ring. This modification is shown in Figure 'I in whichthe groove k is of greater width than the ring, and the spring p issituated in the side ofthe groove remote from the shoe b, so that thelaction of the brake-applying force has no effect on the spring, thelatter` serving merely as a resilient abutment for opposing movement ofthe ring by the shoe.

the spring into engagement with a corresponding hole in the link.

' Instead of employing a4 pair of arms t as above described forpreventing retraction of the shoes b, only one such arm may be employedas shown in Figure 6, this arm being mounted between friction discs ormembers as u on a supporting spindle v carried by one of the shoes b,and the outer end of the arm being connected by a link u to the othershoe. If desired the arm t shown in Figure 6 may be adapted to preventretraction of the shoes b through the medium of a spring similar to thatshown in Figure 8.

Instead of employing a fixed hydraulic cylinder and apair of oppositelymovable pistons y as above described, I may employs cylinder having aclosed end connected to one of the shoes,

and a single piston mounted in the cylinder and operativen' asset-latedwith 'the other shoe. In

this case only one spring ring as above described is required forpreventing retraction of the shoes.

Whilst it is preferredfto employ friction=stops in the form of springrings as above described, these friction stops may take a variety offorms. Thus, as shown in Figure 5, each friction stop may have the formof an arm t pivotally mounted-between friction discs or members as u oua fixed supporting spindle v,- and having its outer end connected by alink w to the adjacent shoe b so that movement of the latter isaccompanied by' pivotal movement of the arm; The friction discs ormembers u are adapted imder the action of spring washers :c to exert asumcient frictional grip on the arms t to prevent retraction of theshoes b from the drum a without offering material resistance tothebrakeapplying force.

If desired each arm t may be adapted to pret is connected to the link wby a projection 2 on the arm engaging a slot 3 in the'link. 'I'he spring'I'he invention is not limited to the examples above described as theconstruction and arrangement of the friction stops may be varied in anumber'of ways., But in all cases the normal tendency of the shoes tomove out of contact i with the complementary brake member formed by thedrum when the brake-applying forceis released is counteracted by thefriction stops. I am aware that friction stops adapted to maintain asubstantially constant clearance space between the shoes and drum whenthe brake is not inaction are well known. My invention differs in thatmy friction stops are adapted to eliminate clearance between thefriction surfaces of the brake.

Having thus described my invention what Iv claim as new and desire tosecure by Letters Patent is: Y A f l. A hydraulically operable frictionbrake having in combination at least one shoe, a complementary brakemember with which the shoe can co-operate, and atleast one friction stopwhich serves to hold the shoe in constant light contact' with thecomplementary brake member when the brake is idle.

f 2. A brake as claimed in claim l and having in combination with thefriction stop, a spring adapted by co-operating with the said stop tooppose retraction of the shoe from the complepiston adapted to actuatethe shoe and provided a has the form of a wire which at a position eintermediate its ends is looped or wound around the pivot spindle v ofthe arm t, and at its Aoppo'- site ends is anchored to the arm and linkrewith a circumferential groove, a hydraulic cylinder containing thepiston, and at least one friction st op in the form of a spring ringmounted in the groove in the piston and adapted by exerting a frictionalgrip on the cylinder'to hold the shoe in constant light contact .withthe complementary brake member when the brake is idle.

5. A brake as claimed in claim 4 and having in combination with thespring ring, a spring also arranged in the groove in the piston andadapted by co-operating with the said ring to oppose retraction of theshoe from the complementary brake member. .6. A hydraulically operablefriction brake having in combination at least one shoe. a complementarybrake member with which the shoe can co-operate, at least onehydraulically operable piston adapted to actuate the shoe, a hydrauliccylinder containing the piston and having in its inner peripheralsurface a circumferential groove which surrounds the piston, and atleast one friction stop in the form of a spring ring mounted in thegroove in the cylinder and adapted by exerting a frictional grip on thepiston to hold the shoe in` constant light contact with thecomplementary brake member when the brake is idle.

7. A brake as claimed in claim 6 and having in combination with thespring ring, a, spring alsoA arranged in the groove in the cylinder andadapted by co-operating with the said ring to oppose retraction of theshoe from the comple- Otal arm mounted on a fixed' axis, a linkconnecting the arm to the shoe, and means adapted to exert a rictionalgrip on and thereby oppose pivotal movement of the arm.

v11. A brake as claimed in claim 1, in which the friction stop comprisesthe combination of a pivotal arm mounted on a fixed axis, a linkconnecting the arm to the shoe, and means adapted to exert a frictionalgrip on and thereby oppose pivotal movement of the arm, the latterhaving combined with it a spring adapted by co-operating with the arm tooppose retraction of the shoe from the complementary brake member.

12. A brake as claimed in claim 1, in which a pair of shoes and a singlefriction stop are provided, and in which the friction stop comprises thecombination of a pivotal arm'mounted on one of the shoes, a linkconnecting the arm to thel other shoe, and means adapted to exert africtional grip on and thereby oppose pivotal movement of the arm. n

13. A brake as claimed in claim 1, in which a pair of shoes and a singlefriction stop are provided, and in which the friction stop comprises thecombination of a pivotal ann mounted on one of the shoes, a linkconnecting the arm to the other shoe, and means adapted to exert africtional grip on and thereby oppose pivotal movement of .the arm, thelatter having combined with it a spring adapted by co-operating with thearm to oppose retraction of the shoes from the complementary brakemember.

POUL ARNE SCOTT-IVERSEN.

